The present invention relates to improvements in gas plasma reactors and the like in which there is deposition or etching of electronic microcircuitry or devices, and, in one particular aspect, to novel and improved dry plasma etching uniformly and simultaneously in a plurality of regions compactly arrayed and uniquely energized to promote optimum quantity and quality of yield from efficiently-used space.
As electronic devices and networks have become reduced in size and proliferated in myriad intricate forms which must be produced with extraordinary precision in vast numbers, thin-film and mirco-line technology and automated expressions of it have correspondingly become increasingly critical. It is well known, for example, that exceedingly thin layers of material can be deposited and shaped to form microscopically-dimensioned details of circuit components, miniature semiconductor devices, or electrical connections, insulation or passageways. Basic techniques for phototgraphically reducing and multiplying such details, and for selectively masking, altering properties, and reacting with the materials involved, have been generally well established in the art for some time; however, needs for ever greater densities of linework having sharper definitions and finer dimensions have increasingly led to exploitations of "dry" reaction techniques which offer alternative attractive prospects for meeting such exacting demands. Unlike wet practices, wherein baths or sprays provide a liquid medium through which depositions or chemical changes or etchings can be induced, comparable dry procedures are conventionally carried out in certain gaseous environments which are activated by applied electrical excitations causing ionizations and glow discharges. By way of example, dry etching may involve ion-bombardment, in which inert ions generated in an RF plasma are accelerated to impinge upon and dislodge atoms from a workpiece, or, in the case of chemical plasma etching, the RF excitation may convert a normally inert gas to a selectively-reactive plasma which diffuses into unmasked workpiece surfaces and develops chemical etching transformations. Plasma etchers of a so-called "planar" configuration are currently preferred in many etching systems, and these include parallel-plate electrodes on which wafers may be rested directly, the supporting plate being made an anode when chemical etching is to dominate and a cathode when a physical or ion-milling type process is to dominate (the latter being known as RIE or reactive ion etching). Even when the wafers are relatively large, however, production one at a time is relatively slow and expensive in such planar etchers, and, when wafers are batched together between large-area electrodes it is difficult to establish operating conditions which will insure that all are uniformly and similarly processed.
The most scrupulous isolation from contaminations is essential in such processing, because even very minute foreign particles or deposits can be ruinous of fine and intricate circuits and devices being processed; high costs of clean-room environments needed to insure such isolations dictate that the dry plasma procedures and equipment should command a very minimum of space. For like economic and quality-control reasons, highly automatic and high-volume production are prime objectives, and it is further advantageous if standard types of cassettes in which wafers are commonly processed into and out of other stages of production can be accommodated also in the dry plasma processing. In addition, it is particularly desirable that electrical and mechanical characteristics of the etching be conducive to the reliable production of uniform-quality precision outputs, in quantity, and that they allow either conventional chemical-type or RIE modes of etching.
Among prior practices which have been described in respect of gas plasma reactors is that involving a pair of planar horizontal electrodes sealed within a housing together with an atmosphere such as carbon tetrafluoride gas and excited by an RF signal to generate a discharge plasma which will etch the surface film on a silicon-base semiconductor wafer, as reviewed in U.S. Pat. No. 4,222,838, for example. Multiple vertically-arranged electrode pairs, of like polarities, were illustrated in the gas plasma etching system of U.S. Pat. No. 4,282,077, together with electrical controls aimed at rendering the etchings of circuit boards more uniform. Cooling of electrodes to improve uniformity has been described in U.S. Pat. No. 4,275,289, and apparatus for automating the transfers of wafers for processing has been disclosed in U.S. Pat. No. 4,062,463.